Polyurethane PSA for sensitive surfaces

ABSTRACT

Polyurethane-based pressure-sensitive adhesive which attaches strongly to polar plastic surfaces, smooth metal surfaces and glass, but which has weak, if any, adhesion to paper, paperboard or skin and is easily detachable without damaging surfaces during its removal, and is reusable. The adhesive comprises a polyurethane formed by reacting an aliphatic or alicyclic polyisocyanate having a functionality of equal to or less than three with a combination of diol and triol.

The invention relates to a pressure-sensitive adhesive (PSA) based on achemically crosslinked polyurethane which attaches well to polarplastics surfaces and smooth metal surfaces and also to glass that showsweak attachment or substantially none at all to paper, paperboard orhuman skin, which in particular is easily removable without damaging thesurfaces during its detachment, and without leaving residues or spotswith a greasy appearance, which, additionally, can be used more thanonce, can be removed by washing and is stable to light, and relates to areactive coating process for its solvent-free and water-free, continuouspreparation, and also relates to the use of the PSA for producingself-adhesive articles, such as adhesive tapes, strips, sheets or pads,for example.

BACKGROUND OF THE INVENTION

Pressure-sensitive adhesion properties or intrinsic adhesion propertiesare not typical of polyurethanes. Although polyurethanes occupy positionfive in the list of plastics, in terms of the amounts produced, PSAs ofthis material play only a very minor role economically.

Nevertheless, polyurethane PSAs have been known for a long time and aredescribed diversely.

The effect of pressure-sensitive adhesiveness can be obtained by addingtackifier resins and/or plasticizers to the polyurethane base polymer.This method is described in, for example, U.S. Pat. No. 3,437,622 A(Dahl et al., Continental Tapes), U.S. Pat. No. 3,718,712 A (Tushaus etal., 3M), U.S. Pat. No. 4,087,392 A (Hartmann et al., BASF), DE 19 04102 A (Hagenweiler, BASF) and JP 2000 256 639 (Toyo).

PSAs of this kind generally have the drawback of not attachingselectively only to certain surfaces. Moreover, following a prolongedperiod of bonding, they unite—usually strongly—with the surfaces andtherefore often cannot be removed.

This “uniting” with the surface is often described by a person skilledin the art as “peel increase”, to describe the increase in bond strengthduring storage of the adhesive bond. It is also possible for thetackifier resin to migrate into the bonded surfaces, where it leavesbehind spots which have a greasy appearance.

High peel increase on numerous surfaces, the resultant difficulty ofredetachment, and the tendency to leave behind spots with a greasyappearance on many surfaces, are observed not least for those PSAs wherethe pressure-sensitive adhesiveness is obtained by undercrosslinking:i.e. an amount of isocyanate groups in deficit to theisocyanate-reactive groups, such as hydroxyl or amino groups, forexample.

PSAs designed on the principle of undercrosslinking are described forexample in U.S. Pat. No. 5,157,101 A (Orr, Norwood), DE 24 35 218 A(Adsley et al., Adhesive Tapes), JP 59 227 922 (Sanyo), U.S. Pat. No.3,930,102 A (Szonn et al., Beiersdorf), U.S. Pat. No. 5,714,543 A(Kydonieus et al., Bristol Myers Squibb), EP 0 597 636 A1 (Kydonieus etal., Squibb) and U.S. Pat. No. 5,591,820 A (Kydonieus et al., Squibb).

Polyurethane PSAs containing monools fall into a very similar categorywith analogous weaknesses. Polyurethanes of this kind are likewiseundercrosslinked and therefore contain relatively large fractions ofmigratable polyurethane units of low molecular weight. Polyurethane PSAson this basis are known for example from EP 0 882 749 A1 (Ikeda et al.,Nitto), U.S. Pat. No. 5,227,409 A (Mobley et al., Dow) and U.S. Pat. No.5,102,714 A (Mobley et al., Dow).

Another type of polyurethane PSAs uses polyol components which carryhydroxyl groups and contain double bonds. Polyurethane PSAs on thisbasis are set out for example in JP 02 003 476 (Tsubota et al., Shinko),WO 98/30648 A1 (Gerard et al., Shell), JP 59 230 076 (Sekisui), JP 2001146 577 (Toyo), U.S. Pat. No. 3,879,248 A (Kest), U.S. Pat. No.3,743,616 A (Kest), U.S. Pat. No. 3,743,617 A (Kest), U.S. Pat. No.5,486,570 A (St. Clair, Shell) and U.S. Pat. No. 3,515,773 A (Dahl etal., Continental Tapes). A drawback is the oxidative sensibility ofthese PSAs, caused by the double bonds in the polymer main chain. Aftera certain time this leads to filming or to “blunting” of thepressure-sensitively adhesive surface. In addition the majority of PSAsof this type additionally contain resins, with the disadvantages alreadydescribed earlier on above.

A special polyurethane PSA containing carbon-carbon double bonds andbased on castor oil, a natural product, is described in U.S. Pat. No.3,246,049 A (Webber, Norton). Here again the oxidative sensitivity is tobe regarded as a weakness.

EP 0 979 835 A (Questel et al., Elf Atochem) proposeshydroxyl-terminated polyalkylenes as a polyol component, which willsolve the problem of oxidative sensitivity. The compositions, however,are moisture-curing, consequently obtain a high ultimate cohesivestrength and cannot be used more than once, so that they are unsuitablefor reversible adhesive bonding of paper. Furthermore they containtackifier resins and plasticizers, whose disadvantages have already beendescribed earlier on above.

Moisture-curing polyurethane PSAs are also described in, for example,U.S. Pat. No. 4,661,542 A (USM), JP 63 189 486 (Sanyo) and EP 0 196 749A1 (von Voithenberg et al., Emhart).

A polyurethane PSA based on hydrogenated polybutadienes is described inJP 01 156 386 (Uehara et al., Hitachi). A drawback there is the need forelectron beam crosslinking, which involves a considerable level oftechnical complexity.

A polyurethane PSA likewise requiring electron beam curing is known fromJP 63 260 917 (Uehara et al., Hitachi). It uses polyethers as a polyolcomponent.

Certain publications describe polyurethane-including blends orpolyurethane copolymers having pressure-sensitive adhesive properties.Examples include U.S. Pat. No. 5,910,536 A (Kydonieus et al., BristolMyers Squibb), U.S. Pat. No. 5,714,543 A (Shah et al., Bristol MyersSquibb) and U.S. Pat. No. 4,626,475 A (Barnett et al., Ashland Oil).These PSAs generally feature a heightened tack and are thereforedifficult to remove from sensitive substrates without damaging them. Asa general rule their pressure-sensitive adhesiveness is not limitedselectively to particular surfaces.

Polyurethane PSAs having special additional properties, such as flameretardancy or electrical conductivity, for example, are described in,for example, EP 1 108 768 A1 (Wong, Tyco) or U.S. Pat. No. 4,855,077 A(Hata et al., Takiron).

Foamed polyurethanes having pressure-sensitive adhesive properties arelikewise known. An example that may be mentioned is the publication DE24 35 217 A (Adsley et al., Adhesive Tapes), and also the descriptionsof hydrophilic foams in DE 42 33 289 A (Kenndoff et al., Beiersdorf) andWO 94/07935 A (Kenndoff et al., Beiersdorf).

In principle, as a result of the enlargement of surface area, foamedpolyurethanes have the drawback of a heightened oxidative sensitivityand also of a heightened light sensitivity. In practice it has beenfound that they exhibit strong peel increase on the majority of surfacesand either cannot be removed without damage or else, particularly in thecase of the foams made hydrophilic by additions of superabsorbent,interact with the substrate in such a way that spotting occurs.

Polyurethanes having pressure-sensitive adhesive properties can also beobtained, as demonstrated in JP 2000 073 040 (Toyo) and JP 2000 256 638(Toyo), by using not only polyethers but also polyesters and also twodifferent catalysts within a polyol component formula. A particulardrawback in this case is the increased preparation complexity resultingfrom the formulas.

JP 2000 328 034 (Toyo), U.S. Pat. No. 3,761,307 A (Dahl) and U.S. Pat.No. 3,925,283 A (Dahl, Continental Tapes) describe pressure-sensitiveadhesive polyurethane/-ureas which are obtained by incorporatingadditional amine-type chain extenders or crosslinkers into the polymer.Drawbacks perceived are the complexity in preparation and the assumedlow selectivity of the pressure-sensitive adhesiveness on differentsurfaces.

DE 21 39 640 A (Dollhausen et al., Bayer) describes a PSA based on anaromatic diisocyanatourethane. A particular drawback is the yellowingtendency, which is typical of aromatic polyurethanes.

In order to achieve pressure-sensitive adhesion properties DE 100 30 908A (Bolte et al., Henkel) and EP 0 081 103 A1 (Miyake et al., Takeda)proposed using two different isocyanates within a polyurethanecomposition. In these cases too the complexity in preparation is foundto be a drawback, as is the low selectivity of the pressure-sensitiveadhesiveness on different surfaces.

WO 97/22642 A1 (Chang et al., Bristol Myers Squibb) proposes, for thepreparation of a PSA, heating an NCO-terminated prepolymer and apolyhydroxy compound together at a certain temperature until a gelfraction of 30 to 40% is obtained. A disadvantage of this method is theassumed low selectivity of the pressure-sensitiveness on differentsurfaces, which results from the relatively low gel content.

U.S. Pat. No. 3,796,678 A (Bartizal, 3M) discloses a polyurethane PSAbased on capped isocyanate prepolymers which relies on water or organicsolvents for its preparation. The complex nature of the preparation isregarded as a drawback, along with the unavoidable need to use water orsolvents.

A polyurethane latex PSA is described in WO 98/31760 A1 (Schrock et al.,Dow Chemical). A drawback is the need for drying, which makes it eitherimpossible or at least very time-consuming to obtain blister-free,relatively thick PSA films.

Certain publications define a polyurethane PSA by way of thecrosslinking density. GB 1,113,925 A (Weller) and GB 1,216,672 A(Grindley) propose chain lengths of 130–285 chain atoms and,respectively, more than 285 chain atoms between the crosslinking points.In practice it has been found that controlling the PSA properties by wayof the criterion of chain length alone is an impossibility. Aninsufficient crosslinking density results in severe peel increase on themajority of substrates after a prolonged bonding period, while too higha crosslinking density leads to PSAs whose pressure-sensitiveadhesiveness is inadequate. Surface-specific selectivity of the PSAproperties is not attained.

EP 1 088 871 A1 (Heguri et al., Sekisui) prescribes a certain distancebetween the isocyanate groups, or a certain degree of crosslinking, forthe polyisocyanate used. The molecular weight between two isocyanategroups in the polyisocyanate is intended to amount to from 220 to 570.This way of controlling the crosslinking density by way of the chainlength within the polyisocyanate is likewise unlikely to improve thesurface-specific selectivity of the PSA properties.

In U.S. Pat. No. 6,040,028 A (Cline et al., Bayer) as well apolyurethane adhesive (contact adhesive) is defined by way of themolecular weight between crosslinking points. A molecular weight ofbetween 7000 and 16000 is prescribed. Further restrictions are imposed,to the effect, inter alia, that from 0 to 10% of the polyols must have amolecular weight of from 60 to 400 and from 90 to 100% of the polyolsmust have a molecular weight of from 1800 to 12000.

Here again it must be assumed that the PSA properties are notselectively surface-specific and that on the majority of substratesthere will be a sharp peel increase following prolonged adhesivebonding, since the crosslinking density is relatively low and noindications of a possible solution to the problem are given.

WO 01/62818 A1 (Hansen et al., 3M) proposes reacting two polyols orother NCO-reactive materials with isocyanates for the preparation of apolyurethane PSA, the isocyanate-reactive components differing from oneanother in that one has a molecular weight of more than 2000 and one hasa molecular weight of less than 2000.

PSAs of this kind are known inter alia from the examples in U.S. Pat.No. 5,227,409 A and U.S. Pat. No. 3,437,622 A, which also includes therestriction (claim 5) whereby the isocyanate-reactive components arealmost exclusively diols. Additionally, polyurethanes with such acomposition have already been described in the examples in EP 1 095 993A1 and EP 1 101 803 A1, the last-mentioned examples not relating tocompositions intended for the obtainment of PSAs. The proposed reactionproduct in WO 01/62818 A1 is therefore not definitively a PSA. There areno references to a surface-specific selectivity of the PSA properties.

It is an object of the invention to provide a pressure-sensitiveadhesive which adheres well to polar plastics surfaces and smooth metalsurfaces and also to glass, which in particular is easy to remove,without damaging surfaces during its detachment, particularly when thesurfaces are sensitive to mechanical influences, and which does notdisplay the above-described drawbacks of the prior art, or not to thesame extent. In particular it should show substantially no adhesion oronly very little adhesion to paper, paperboard or similar materials andalso to human skin, should essentially not feel tacky, should not leaveany residues or spots of greasy appearance following its removal, andshould also be able to be used more than once, removed by washing andstable to light.

SUMMARY OF THE INVENTION

The invention accordingly provides a pressure-sensitive adhesive basedon polyurethane wherein the polyurethane is composed of the followingstarting materials which are reacted catalytically with one another inthe stated proportions:

-   -   a) at least one aliphatic or alicyclic polyisocyanate having a        functionality of in each case less than or equal to three,    -   b) a combination of at least one polypropylene glycol diol and        at least one polypropylene glycol triol,        -   the ratio of the number of hydroxyl groups in the diol            component to the number of hydroxyl groups in the triol            component being less than 10, preferably between 0.2 and 5,        -   additionally the ratio of the number of isocyanate groups to            the total number of hydroxyl groups being between 0.8 and            1.15, preferably between 0.95 and 1.05, more preferably            between 1.0 and 1.05,        -   the catalyst for the reaction to the polyurethane consisting            of or comprising a bismuth carboxylate or bismuth            carboxylate derivative, and        -   the diols and triols alternatively being selected and            combined in each case as follows:            -   diols having a molecular weight of less than or equal to                1000 are combined with triols whose molecular weight is                greater than or equal to 1000, preferably greater than                or equal to 3000,            -   diols having a molecular weight of greater than 1000 are                combined with triols whose molecular weight is less than                1000.

In order to produce polyurethanes having sufficient light stability itis necessary, as is known, to use aliphatic or alicyclic polyisocyanatesor polyisocyanates containing isocyanate groups which are notaromatically attached. Surprisingly it has been found that aliphatic oralicyclic polyisocyanates are suitable for producing the other desiredproperties of the polyurethane PSAs in accordance with the object of theinvention. The surface-specific selectivity of the PSA properties inparticular can be adjusted to the use of aliphatic or alicyclicpolyisocyanates.

DETAILED DESCRIPTION

In one advantageous embodiment aliphatic or alicyclic diisocyanates areused. Particularly advantageous is the use of aliphatic or alicyclicdiisocyanates having in each case an asymmetrical molecular structure,in which, therefore, the two isocyanate groups each possess a differentreactivity. In particular the tendency otherwise typically found withpressure-sensitive adhesive polyurethanes, namely that of leaving spotsof greasy appearance on paper or paperboard, is markedly reduced throughthe use of aliphatic or alicyclic diisocyanates having an asymmetricmolecular structure. By an asymmetric molecular structure is meant theabsence from the molecule of elements of symmetry (for example mirrorplanes, axes of symmetry, centres of symmetry); in other words, theimpossibility of performing any symmetry operation to produce a moleculecongruent with the starting molecule.

Examples of suitable polyisocyanates in accordance with the inventionare butane 1,4-diisocyanate, tetramethoxybutane 1,4-diisocyanate, hexane1,6-diisocyanate, ethylene diisocyanate, 2,2,4-trimethylhexamethylenediisocyanate, ethylethylene diisocyanate, dicyclohexylmethanediisocyanate, 1,4-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane,1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclopentane,1,2-diisocyanatocyclopentane, 1,2-diisocyanatocyclobutane,1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (isophoronediisocyanate), 1-methyl-2,4-diisocyanato-cyclohexane,1,6-diisocyanato-2,2,4-trimethylhexane,1,6-diisocyanato-2,4,4-trimethylhexane,5-isocyanato-1-(2-isocyanatoeth-1-yl)-1,3,3-trimethylcyclohexane,5-isocyanato-1-(3-isocyanatoprop-1-yl)-1,3,3-trimethylcyclohexane,5-isocyanato-1-(4-isocyanato 1-yl)-1,3,3-trimethylcyclohexane,1-isocyanato-2-(3-isocyanatoprop-1-yl)cyclohexane,1-isocyanato-2-(2-isocyanatoeth-1-yl)cyclohexane,2-heptyl-3,4-bis(9-isocyanatononyl)-1-pentylcyclohexane, norbornanediisocyanatomethyl, chlorinated, brominated, sulphur-containing orphosphorus-containing aliphatic or alicyclic diisocyanates, and alsoderivatives of the diisocyanates listed, especially dimerized ortrimerized types.

In one particularly preferred embodiment isophorone diisocyanate isused.

With regard to the substantive and quantitative composition of thestarting materials reacted with the polyisocyanate it has surprisinglybeen found that combinations of at least one polypropylene glycol dioland at least one polypropylene glycol triol are suitable for producingpolyurethanes having the desired profile of properties in accordancewith the object of the invention, if the ratio of the number of hydroxylgroups in the diol component to the number of hydroxyl groups in thetriol component is less than 10, preferably between 0.2 and 5.0, if,additionally, the ratio of the number of isocyanate groups to the totalnumber of hydroxyl groups is between 0.8 and 1.15, preferably between0.95 and 1.05, more preferably between 1.0 and 1.05, if the catalyst forthe reaction to the polyurethane consists of or comprises a bismuthcarboxylate or a bismuth carboxylate derivative, and if the diols andtriols are alternatively in each case selected and combined as follows:

-   -   diols having a molecular weight of less than or equal to 1000        are combined with triols whose molecular weight is greater than        or equal to 1000, preferably greater than or equal to 3000,    -   diols having a molecular weight of greater than 1000 are        combined with triols whose molecular weight is less than 1000.

As polypropylene glycols it is possible to use all commerciallycustomary polyethers based on propylene oxide and a starter which isdifunctional in the case of the diols and trifunctional in the case ofthe triols. Included here are not only the polypropylene glycolsprepared conventionally—that is, generally, using a basic catalyst, suchas potassium hydroxide, for example—but also the particularly purepolypropylene glycols prepared by DMC (Double metal cyanide) catalysis,whose preparation is described in, for example, U.S. Pat. No. 5,712,216A, U.S. Pat. No. 5,693,584 A, WO 99/56874 A1, WO 99/51661 A1, WO99/59719 A1, WO 99/64152 A1, U.S. Pat. No. 5,952,261 A, WO 99/64493 A1and WO 99/51657 A1.

A characteristic of the DMC-catalyzed polypropylene glycols is that the“nominal” or theoretical functionality of precisely 2 in the case of thediols or precisely 3 in the case of the triols is also actually achievedapproximately.

In the case of the conventionally prepared polypropylene glycols the“true” functionality is always somewhat lower than the theoreticalfunctionality, particularly in the case of polypropylene glycols havinga relatively high molecular weight. The reason for this is a secondaryreaction of rearrangement of the propylene oxide to form allyl alcohol.

It is also possible to use all polypropylene glycol diols or triolscontaining copolymerized ethylene oxide, which is the case in manycommercially customary polypropylene glycols, in order to obtain anincreased reactivity towards isocyanates.

By varying the ratio of the number of hydroxyl groups in the diol tothat in the triol within the stated boundaries it is possible toinfluence the bond strength and to adjust it in accordance with theapplication. Surprisingly it has been found that the higher the ratio ofthe number of diol OH groups to the number of triol OH groups thegreater the bond strength.

The bond strength range which can be set within the stated boundaries isapproximately up to 3.0 N/cm, measured on steel in accordance withPSTC-101 (see description of the test methods).

Surprisingly it has been found that the use of a catalyst or catalystmixture comprising bismuth carboxylate or a bismuth carboxylatederivative, the use of which catalyst or mixture is known for theacceleration of polyurethane reactions, exerts considerable control overthe PSA properties of the polyurethane in a manner such that theyachieve a surface-specific selectivity.

Examples of bismuth carboxylates are bismuth trisdodecanoate, bismuthtrisdecanoate, bismuth trisneodecanoate, bismuth trisoctanoate, bismuthtrisisooctanoate, bismuth trishexanoate, bismuth trispentanoate, bismuthtrisbutanoate, bismuth trispropanoate and bismuth trisacetate.

In one possible embodiment the polyurethane-based PSA includes furtherformulating ingredients such as, for example, additional catalysts,ageing inhibitors (antioxidants), light stabilizers such as, forexample, UV absorbers, rheological additives, and other auxiliaries andadditives.

In the selection of these substances it should be ensured that they donot have any tendency to migrate to the substrate to be bonded, so thatthere is no spotting occurring in this way. For the same reason theconcentration of these substances, particularly the liquid substances,in the composition as a whole is to be kept as low as possible. Theadditional use of plasticizers or tackifier resins should therefore beavoided, without any intention thereby to exclude these substancesentirely.

In order further to accelerate the reaction between the isocyanatecomponent and the isocyanate-reactive component it is possible inaddition to use any of the catalyst known to the person skilled in theart, such as tertiary amines or organotin compounds, for example.

The use of antioxidants, though advantageous, is not mandatory.

Suitable antioxidants include for example sterically hindered phenols,hydroquinone derivatives, sterically hindered amines, organic sulphurcompounds and organic phosphorus compounds.

Light stabilizers or UV absorbers can also optionally be used.

Light stabilizers used are those disclosed in Gaechter and Müller,Taschenbuch der Kunststoff-Additive, Munich, 1979, in Kirk-Othmer (3.)23, 615 to 627, in Encycl. Polym. Sci. Technol. 14, 125 to 148 and inUllmann (4.) 8, 21; 15, 259, 676.

Examples of rheological additives are pyrogenic silicas, phyllosilicates(for example bentonites), high molecular mass polyamide powders orcastor oil derivative powders.

In one preferred embodiment the pressure-sensitive adhesive is preparedcontinuously in accordance with the process described below:

A vessel A is charged substantially with the premixed polypropyleneglycol combination (polyol component) and a vessel B is chargedsubstantially with the isocyanate component, it being possible for theother formulating ingredients to have been mixed into these componentsbeforehand in a standard mixing procedure.

The polyol component and the isocyanate component are conveyed viaprecision pumps through the mixing head or mixing tube of amulti-component mixing and metering unit, where they are homogenouslymixed and so brought to reaction. The chemically inter-reactivecomponents mixed in this way are applied immediately thereafter to asheet-like backing material which is preferably moving at a constantspeed. The nature of the backing material depends on the article to beproduced. The backing material coated with the reactive polyurethanecomposition is passed through a heating tunnel in which the polyurethanecomposition cures to the PSA. The coatweight of the polyurethanecomposition is freely selectable. It depends on the article to beproduced. Finally the coated backing material is wound up in a windingstation.

The process described allows solvent-free and water-free operation.Solvent-free and water-free operation is the preferred procedure, but isnot mandatory. In order, for example, to obtain particularly lowcoatweights, the components can be diluted appropriately.

In order to enhance the anchorage of the polyurethane composition on thesheet-like backing materials it is possible to use any known method ofsurface treatment, such as Corona pretreatment, flaming, gas-phasetreatment (fluorination, for example). It is possible to use any knownmethods of priming, in which case the primer layer can be applied eitherfrom solution or dispersion to the backing material or else in anextrusion or coextrusion process.

In order to improve the unwind properties of the wound roll it ispossible to precoat the reverse of the sheet-like material with arelease coating material or for the reverse to carry a co-extruded orextruded-on release coating.

A polyurethane-based pressure-sensitive adhesive as described abovewherein the polyurethane is composed of the following starting materialswhich are reacted with one another in the stated proportions:

-   a) at least one aliphatic or alicyclic polyisocyanate having a    functionality of in each case less than or equal to three,-   b) a combination of at least one polypropylene glycol diol and at    least one polypropylene glycol triol,    -   the ratio of the number of hydroxyl groups in the diol component        to the number of hydroxyl groups in the triol component being        less than 10, preferably between 0.2 and 5.0,    -   additionally the ratio of the number of isocyanate groups to the        total number of hydroxyl groups being between 0.8 and 1.15,        preferably between 0.95 and 1.05, more preferably between 1.0        and 1.05,    -   the catalyst for the reaction to the polyurethane consisting of        or comprising a bismuth carboxylate or bismuth carboxylate        derivative, and    -   the diols and triols alternatively being selected and combined        in each case as follows:        -   diols having a molecular weight of less than or equal to            1000 are combined with triols whose molecular weight is            greater than or equal to 1000, preferably greater than or            equal to 3000,        -   diols having a molecular weight of greater than 1000 are            combined with triols whose molecular weight is less than            1000,            exhibits outstanding product properties which even the            person skilled in the art could have not foreseen in such a            way.

The pressure-sensitive adhesive is suitable for fastening or fixingsmall articles, for example, having sensitive surfaces of polar plastic,glass or metal in such a way that on the one hand these articles areheld securely while on the other hand they can be removed withoutproblems at any time, very substantially without the PSA which is nowopen, i.e., is no longer covered, causing disruption as a result of ahigh intrinsic tack and without the surfaces of the articles beingdamaged, contaminated or destroyed by the operation of adhering andremoving. The PSA can be used as part of an overall bonding scheme forthe adhesive bonding of articles in magazines, books, letters or topapers in general and after the articles have been detached can remainin the magazines, books, letters or papers in general, since it adheresvery weakly if at all to these substrates and consequently there is nosubsequent sticking together, or at least no irreversible stickingtogether, of individual pages in the magazines, books, letters ormutually superposed papers in general. Since the pressure-sensitiveadhesive as described above also exhibits substantially no adhesion, orat least only weak adhesion, to human skin as well, there is nounpleasant sensation of stickiness on contact.

Following the detachment operation the PSA does not leave behind anyresidues or spots of greasy appearance on the articles and does notdamage the articles, and in particular does not do so even when thesearticles are sensitive to mechanical influences, which is often the casewith articles having very smooth surfaces.

The pressure-sensitive adhesive as described above can be used more thanonce without impairment to its bond strength. If the PSA is stored inthe unbonded state in a normal environment for a prolonged periodwithout a protective colouring, it naturally becomes dusty, and its bondstrength is reduced as a result. Such a layer of dust can easily beremoved again at any time using normal mains water. After drying, theoriginal bond strength is immediately reestablished in full. Even largequantities of dust, sand or powders of all grain sizes can easily beremoved again by washing.

By virtue of the fact that the PSA is stable to light, it can also beused for adhesive bonding on articles, materials or substrates which areexposed to light and sun, for example on or behind windowpanes or carwindows. In general the PSA is equally suitable for both interior andexterior applications.

The intention of the text below is to illustrate the invention withreference to examples, though without wishing to thereby to restrict it.

The following test methods were used briefly to characterize thespecimens produced in accordance with the processes described.

-   -   The test specimens were each produced by coating the initially        liquid, reactive polyurethane PSA at a coatweight of 50 g/m²        onto a 26 μm polyester film and curing it at 100° C. The        measurements were made after an “ageing period” (at room        temperature) of one week.    -   The bond strength was determined in accordance with PSTC-101        (peel adhesion). In accordance with this method the assembly of        PSA layer and polyester film is applied to different substrates        (steel, ABS, PS, PVC, PP) and then peeled under defined        conditions by means of a tensile testing machine. The peel angle        is in each case 180° and the peel speed 300 mm/min. The force        required for peeling is the bond strength, which is reported        with the units N/cm.    -   The tack measurement (measurement of the surface stickiness) was        made by the die measurement method in accordance with ASTM D        2979-01 using the texture analyser TA 2 from the company SMS        (Stable Micro Systems). In accordance with this method a        cylindrical steel die is pressed with defined force and rate up        to the sample under analysis and is removed again after a        defined time at a defined rate. The test result is the maximum        force required for its removal, reported with the units N.

The specific test parameters were as follows:

cylinder radius: 1 mm

cylinder area: 3.14 mm² pressing rate:  0.1 mm/s pressing force:   5 Npressing time: 0.01 s removal rate:  0.6 mm/s

-   -   The testing of light stability was carried out using a so-called        sunlight lamp from Osram with the designation ULTRA-VITALUX®,        power output 300 W. The samples were uninterruptedly irradiated        open from a distance of 50 cm. The temperature of the location        of the samples was in each case approximately 60° C. Assessments        were made of the colour change of the PSA and also of the change        in bond strength in each case after a period of irradiation of        one week and of two weeks. This corresponds approximately in        each case to a 10-fold uninterrupted real summer sun exposure in        central Europe.

EXAMPLES

Coating in the examples was carried out on a standard laboratory coatingunit for continuous coating. The sheet width was 50 cm. The coating slotwidth was variably adjustable between 0 and 1 cm. The length of theheating tunnel was about 12 m. The temperature in the heating tunnel wasdivisible into four zones each freely selectable between roomtemperature and 120° C.

A standard multi-component mixing and metering unit with a dynamicmixing system was used. The mixing head was designed for two liquidcomponents. The mixing rotor had a variable speed of up to approximately5000 rpm max. The metering pumps of this unit were gear pumps having anoutput of approximately 2 l/min max.

The polyol components were prepared in a standard heatable and evacuablemixing tank. During the mixing operation, which took about two hours ineach case, the temperature of the mixture was set at about 70° C. and avacuum was applied in order to degas the components.

Table 1 lists the base materials used to prepare the polyurethane PSAs,in each case with their trade names and manufacturer. The raw materialscited are all freely available commercially.

TABLE 1 Base materials used to prepare the polyurethane PSAs, with tradename and manufacturer Chemical basis Average molar mass Trade name OH orNCO number Manufacturer/supplier Desmophen 1262 BD ® Polypropyleneglycol, Bayer Diol (M = 430) (4661 mmol OH/kg) Desmophen 1112 BD ®Polypropylene glycol, Bayer Diol (M = 1000) (1977 mmol OH/kg) Acclaim4220 N ® Polypropylene glycol, Bayer Diol, high-purity, prepared by DMCcatalysis (M = 4000) (500 mmol OH/kg) Desmophen 1380 BT ® Polypropyleneglycol, Bayer Triol (M = 450) (6774 mmol OH/kg) Desmophen 3061 BT ®Polypropylene glycol, Bayer Triol (M = 3000) (1000 mmol OH/kg) Desmophen5035 BT ® Polypropylene glycol, Bayer Triol (M = 4800) (624 mmol OH/kg)Acclaim 6320 N ® Polypropylene glycol, Bayer Triol, high-purity,prepared by DMC catalysis (M = 6000) (500 mmol OH/kg) Vestanat IPDI ®Isophorone diisocyanate Degussa-Hüls (M = 222.3) (8998 mmol NCO/kg)Vestanat TMDI ® 2,2,4-Trimethylhexamethylene Degussa-Hüls diisocyanate(M = 210.3) (9500 mmol NCO/kg) Desmodur N 3300 ® Aliphaticpolyisocyanate based on Bayer hexamethylene diisocyanate (5143 mmolNCO/kg) Desmodur W ® Dicyclohexylmethane diisocyanate Bayer (M = 262)(7571 mmol NCO/kg) Bismuth trisneodecanoate CAS No. 34364-26-6 MarkDBTL ® Dibutyltin dilaurate Nordmann, Rassmann Tinuvin 292 ® Stericallyhindered amine, light stabilizer Ciba Tinuvin 400 ® Triazine derivative,UV stabilizer Ciba Aerosil R202 ® Hydrophobicized pyrogenic silicaDegussa-Hüls

Example 1

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 12.156.3 mmol OH Acclaim 6320 N ® 75.1 37.5 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 10.6 95.7 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.15 N/cm on steel,    -   0.23 N/cm on ABS,    -   0.36 N/cm on PS,    -   0.41 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.4 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 2

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 12.357.4 mmol OH Acclaim 6320 N ® 76.6 38.3 mmol OH Bismuth 0.3trisneodecanoate B component Vestanat IPDI ® 10.8 97.6 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.17 N/cm on steel,    -   0.22 N/cm on ABS, 0.31 N/cm on PS,    -   0.44 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.4 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. After two weeks of irradiation there were nocolour changes, but the inherent tack was now distinctly perceptible.The bond strength (on steel) was now 1.6 N/cm.

The adhesion to paper and paperboard was extremely low. The PSA wasremovable from the substrates simply by shaking. The PSA was stuck intoa number of books, newspapers and magazines. Even after a bonding periodof six months, the pages bonded in this way were readily removable fromone another and the PSA could be removed readily without leavingresidues or greasy spots and without damaging the papers. The PSA didnot stick to the skin. Moreover, the PSA was removable by washing. Forthe purpose of testing it was sprinkled with fine-grained sand and, in asecond test, with fine-grained talc. Both substances were easilyremovable again under running water. Subsequently the bond strength wasat the original level. Repeat usability was tested by adhering the PSAto PVC and removing it again 20 times in succession. Thereafter the bondstrength was still at the original level.

Example 3

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 2.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 17.9 83.3 mmol OH Acclaim 6320 N ® 66.7  33.3 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 13.2 119.0 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.19 N/cm on steel,    -   0.25 N/cm on ABS,    -   0.47 N/cm on PS,    -   0.53 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.5 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 4

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 4.0Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 24.5114.2 mmol OH Acclaim 6320 N ® 57.1  28.6 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 16.2 145.6 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.26 N/cm on steel,    -   0.53 N/cm on ABS,    -   0.68 N/cm on PS,    -   0.76 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.7 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 5

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.05 Ratio of number of diol OH/number of triol OH: 10.0Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 38.6180.1 mmol OH Acclaim 6320 N ® 36.0  18.0 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 23.2 208.0 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.53 N/cm on steel,    -   1.13 N/cm on ABS,    -   0.95 N/cm on PS,    -   1.18 N/cm on PVC.

The tack measurement (on steel) gave a figure of 1.3 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 6

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.0Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 10.347.8 mmol OH Desmophen 5035 BT ® 76.7 47.8 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 10.8 97.6 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.13 N/cm on steel,    -   0.22 N/cm on ABS,    -   0.36 N/cm on PS,    -   0.32 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.3 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 7

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.0Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 10.548.8 mmol OH Desmophen 5035 BT ® 78.2 48.8 mmol OH Bismuth 0.3trisneodecanoate B component Vestanat IPDI ® 11.0 99.5 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.15 N/cm on steel,    -   0.28 N/cm on ABS,    -   0.46 N/cm on PS,    -   0.38 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.3 N. After a week ofirradiation with the sunlight lamp there were no changes, either incolour or in bond strength. After two weeks of irradiation there were nocolour changes, but the inherent tack was now distinctly perceptible.The bond strength (on steel) was now 1.8 N/cm.

The adhesion to paper and paperboard was extremely low. The PSA wasremovable from the substrates simply by shaking. The PSA was stuck intoa number of books, newspapers and magazines. Even after a bonding periodof six months, the pages bonded in this way were readily removable fromone another and the PSA could be removed readily without leavingresidues or greasy spots and without damaging the papers. The PSA didnot stick to the skin. Moreover, the PSA was removable by washing. Forthe purpose of testing it was sprinkled with fine-grained sand and, in asecond test, with fine-grained talc. Both substances were easilyremovable again under running water. Subsequently the bond strength wasat the original level. Repeat usability was tested by adhering the PSAto PVC and removing it again 20 times in succession. Thereafter the bondstrength was still at the original level.

After one week of irradiation with the sunlight lamp there were nochanges, either in colour or in bond strength. After two weeks ofirradiation there were no changes in colour, but the PSA was markedlysofter. The inherent tack had increased. The bond strength was now 7.9N/cm.

Example 8

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 14.3 66.5 mmol OH Desmophen 5035 BT ® 71.0  44.3 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 12.6 113.0 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.21 N/cm on steel,    -   0.34 N/cm on ABS,    -   0.52 N/cm on PS,    -   0.48 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.5 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 9

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 2.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 20.7 96.4 mmol OH Desmophen 5035 BT ® 61.8  38.6 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 15.3 137.6 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.31 N/cm on steel,    -   0.62 N/cm on ABS,    -   0.58 N/cm on PS,    -   0.52 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.7 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 10

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 4.0Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 27.7129.3 mmol OH Desmophen 5035 BT ® 51.8  32.3 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 18.3 164.8 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.42 N/cm on steel,    -   0.81 N/cm on ABS,    -   0.68 N/cm on PS,    -   0.73 N/cm on PVC.

The tack measurement (on steel) gave a figure of 1.0 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 11

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 0.90 Ratio of number of diol OH/number of triol OH: 0.3Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 5.324.6 mmol OH Desmophen 3061 BT ® 81.9 81.9 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 10.6 95.8 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.41 N/cm on steel,    -   0.43 N/cm on ABS,    -   0.51 N/cm on PS,    -   0.51 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.5 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 12

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 0.95 Ratio of number of diol OH/number of triol OH: 0.7Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 11.1 51.5 mmol OH Desmophen 3061 BT ® 73.5  73.5 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 13.2 118.8 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.63 N/cm on steel,    -   0.51 N/cm on ABS,    -   0.49 N/cm on PS,    -   0.52 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.5 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 13

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 0.95 Ratio of number of diol OH/number of triol OH: 1.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 19.9 92.2 mmol OH Desmophen 3061 BT ® 61.7  61.7 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 16.2 146.5 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.72 N/cm on steel,    -   0.81 N/cm on ABS,    -   0.55 N/cm on PS,    -   0.76 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.8 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 14

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 2.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 18.0 83.9 mmol OH Acclaim 6320 N ® 67.2  33.6 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat TMDI ® 12.6 119.9 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.32 N/cm on steel,    -   0.31 N/cm on ABS,    -   0.45 N/cm on PS,    -   0.49 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.6 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 15

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 2.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 16.2 75.6 mmol OH Acclaim 6320 N ® 60.6  30.3 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Desmophen N 3300 ® 21.0 108.0 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.18 N/cm on steel,    -   0.21 N/cm on ABS,    -   0.31 N/cm on PS,    -   0.26 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.3 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 16

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 2.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 17.5 81.2 mmol OH Acclaim 6320 N ® 65.0  32.5 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Desmodur W ® 15.3 116.0 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.15 N/cm on steel,    -   0.23 N/cm on ABS,    -   0.18 N/cm on PS,    -   0.21 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.3 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 17

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 2.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1112 BD ® 48.7 96.1 mmol OH Desmophen 3061 BT ® 34.3  34.3 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 14.8 133.1 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.21 N/cm on steel,    -   0.31 N/cm on ABS,    -   0.56 N/cm on PS,    -   0.68 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.5 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 18

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 4.0Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1112 BD ® 43.1 85.1 mmol OH Acclaim 6320 N ® 42.6  21.3 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 12.1 108.6 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.53 N/cm on steel,    -   0.82 N/cm on ABS,    -   0.93 N/cm on PS,    -   1.12 N/cm on PVC.

The tack measurement (on steel) gave a figure of 1.1 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 19

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 0.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Acclaim 4220 N ® 74.1 37.0 mmol OH Desmophen 1380 BT ® 11.1  74.1 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 12.6 113.4 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.43 N/cm on steel,    -   0.62 N/cm on ABS,    -   0.81 N/cm on PS,    -   0.79 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.9 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 20

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.5Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 4220 N ® 85.442.7 mmol OH Desmophen 1380 BT ® 4.3 28.6 mmol OH Bismuth 0.3trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0B component Vestanat IPDI ® 8.1 72.6 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.92 N/cm on steel,    -   1.13 N/cm on ABS,    -   1.10 N/cm on PS,    -   0.95 N/cm on PVC.

The tack measurement (on steel) gave a figure of 1.2 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 21

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.5Ratio of number of diol short-chain OH/number of diol long-chain OH: 1.0Number of OH or Weight NCO groups fraction based on the [% by percentageweight Ingredient weight] fraction A component Desmophen 1262 BD ® 5.626.0 mmol OH Desmophen 1112 BT ® 13.1 26.0 mmol OH Acclaim 6320 N ® 69.334.6 mmol OH Bismuth 0.3 trisneodecanoate Tinuvin 292 ® 0.3 Tinuvin400 ® 0.6 Aerosil R202 ® 1.0 B component Vestanat IPDI ® 9.8 88.3 mmolNCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.52 N/cm on steel,    -   0.61 N/cm on ABS,    -   0.92 N/cm on PS,    -   0.83 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.7 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 22

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.5Ratio of number of triol short-chain OH/number of triol long-chain OH:2.0 Number of OH or Weight NCO groups fraction based on the [% bypercentage weight Ingredient weight] fraction A component Desmophen 1262BD ® 16.3  75.7 mmol OH Desmophen 3061 BT ® 33.6  33.6 mmol OH Acclaim6320 N ® 33.6  16.8 mmol OH Bismuth 0.3 trisneodecanoate Tinuvin 292 ®0.3 Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0 B component Vestanat IPDI ®14.3 128.7 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.30 N/cm on steel,    -   0.41 N/cm on ABS,    -   0.32 N/cm on PS,    -   0.27 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.3 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

Example 23

The composition of the inventive polyurethane PSA is as follows:

NCO/OH ratio: 1.02 Ratio of number of diol OH/number of triol OH: 1.0Ratio of number of NCO (IPDI)/NCO (TMDI): 2.0 Number of OH or Weight NCOgroups fraction based on the [% by percentage weight Ingredient weight]fraction A component Desmophen1262 BD ® 8.6 40.1 mmol OH Acclaim 6320N ® 80.2 40.1 mmol OH Bismuth 0.3 trisneodecanoate Tinuvin 292 ® 0.3Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0 B component Vestanat IPDI ® 6.154.6 mmol NCO Vestanat TMDI 2.9 27.3 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film;see above) achieved the following bond strengths:

-   -   0.14 N/cm on steel,    -   0.27 N/cm on ABS,    -   0.39 N/cm on PS,    -   0.48 N/cm on PVC.

The tack measurement (on steel) gave a figure of 0.4 N. After two weeksof irradiation with the sunlight lamp there were no changes, either incolour or in bond strength. The adhesion to paper and paperboard wasextremely low. The PSA was removable from the substrates simply byshaking. The PSA was stuck into a number of books, newspapers andmagazines. Even after a bonding period of six months, the pages bondedin this way were readily removable from one another and the PSA could beremoved readily without leaving residues or greasy spots and withoutdamaging the papers. The PSA did not stick to the skin. Moreover, thePSA was removable by washing. For the purpose of testing it wassprinkled with fine-grained sand and, in a second test, withfine-grained talc. Both substances were easily removable again underrunning water. Subsequently the bond strength was at the original level.Repeat usability was tested by adhering the PSA to PVC and removing itagain 20 times in succession. Thereafter the bond strength was still atthe original level.

COMPARATIVE EXAMPLES Comparative Example 1

Polyurethane composition: NCO/OH ratio: 0.95 Ratio of number of diolOH/number of triol OH: 5.0 Number of OH or Weight NCO groups fractionbased on the [% by percentage weight Ingredient weight] fraction Acomponent Desmophen 1262 BD ® 31.8   148 mmol OH Desmophen 5035 BT ®47.3  29.5 mmol OH Mark DBTL ® 0.3 Tinuvin 292 ® 0.3 Tinuvin 400 ® 0.6Aerosil R202 ® 1.0 B component Vestanat IPDI ® 18.7 168.6 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film,see above) achieved a bond strength on steel of 7.4 N/cm. The PSA bondedvery strongly to paper, and so could by no means be removed from thepaper simply by shaking. It likewise bonded very strongly to the skin.

Comparative Example 2

Polyurethane composition: NCO/OH ratio: 0.7 Ratio of number of diolOH/number of triol OH: 2.5 Number of OH or Weight NCO groups fractionbased on the [% by percentage weight Ingredient weight] fraction Acomponent Desmophen 1262 BD ® 21.7 101.3 mmol OH Desmophen 5035 BT ®65.0  40.5 mmol OH Bismuth 0.3 trisneodecanoate Tinuvin 292 ® 0.3Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0 B component Vestanat IPDI ® 11.1 99.3 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film,see above) achieved a bond strength on steel of 8.2 N/cm. The PSA bondedvery strongly to paper, and so could by no means be removed from thepaper simply by shaking. In addition it left spots of greasy appearanceon the paper after just a short time. It additionally bonded verystrongly to the skin.

Comparative Example 3

Polyurethane composition: NCO/OH ratio: 1.02 Ratio of number of diolOH/number of triol OH: 1.0 Number of OH or Weight NCO groups fractionbased on the [% by percentage weight Ingredient weight] fraction Acomponent Desmophen 1262 BD ® 35.6 166.0 mmol OH Desmophen 1380 BT ®24.6 166.0 mmol OH Bismuth 0.3 trisneodecanoate Tinuvin 292 ® 0.3Tinuvin 400 ® 0.6 Aerosil R202 ® 1.0 B component Vestanat IPDI ® 37.6338.6 mmol NCO

The test specimens (50 g/m² polyurethane PSA on 26 μm polyester film,see above) achieved a bond strength on steel and on plastics of lessthan 0.1 N/cm. The bond strength was too low to fix lightweight plasticparts.

1. A pressure-sensitive adhesive comprising the product of the catalyticreaction of: a) at least one aliphatic or alicyclic polyisocyanatehaving a functionality of less than or equal to three, b) a combinationof at least one polypropylene glycol diol and at feast one polypropyleneglycol triol, the ratio of the number of hydroxyl groups in the diolcomponent to the number of hydroxyl groups in the triol component beingless than 10 the ratio of the number of isocyanate groups to the totalnumber of hydroxyl groups being between 0.8 and 1.15, the catalyst forthe reaction consisting of or comprising a bismuth carboxylate orbismuth carboxylate derivative, and the diols having a molecular weightof less than or equal to 1000 and the triols having a molecular weightgreater than or equal to
 1000. 2. Pressure-sensitive adhesive accordingto claim 1, wherein said at least one aliphatic or alicyclicpolyisocyanates are diisocyanates.
 3. Pressure-sensitive adhesiveaccording to claim 1 wherein said polyisocyanate is selected from thegroup consisting of butane 1,4-diisocyanate, tetramethoxybutane1,4-diisocyanate, hexane ,1,6-diisocyanate, ethylene diisocyanate,2,2,4-trimethylhexamethylene d iisocyanate, ethylethylene diisocyanate,dicyclohexylmethane diisocyanate, ,1,4-diisocyanatocyclohexane,1,3-diisocyanatocyclohexane, 1,2-diisocyanatocyclohexane,1,3-diisocyanatocyclopentane, 1,2-diisocyanatocyclopentane,1,2-diisocyanatocyolobutane,1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclo-hexane (isophoronediisocyanate), 1-methyl-2,4-diisocyanato-cyclohexane,1,6-diisocyanato-2,2,4-trimethylhexane1,6-diisocyanato-2,4,4-trimethylhexane, 5-isocyanato-1-(2-isocyanatoeth-1-yl)-1,3,3-trimethylcyolohexane, 5-isocyanato-1-(3-isooyanatoprop-1-yl)-1,3,3-trimethylcyclohexane,5-isocyanato-1-(4-isocyanatobut-1 -yl)-1,3,3-trimethylcyclohexane,1-isocyanato-2-(3-isocyanatoprop-1-yl)cyclohexane, 1-isocyanato-2-(2-isooyanatoeth-1-yl)cyclohexane,2-heptyl-3,4-bis(9-isocyanatononyl)-1-pentylcyclohexane, norbornanediisocyanatomethyl, chlorinated aliphatic or alicyclic diisocyanates,brominated aliphatic or alicyclic diisocyanates, sulphur-containingaliphatic or alicyclic diisocyanates, phosphorus-containing aliphatic oralicyclic diisocyanate and derivatives thereof.
 4. Pressure-sensitiveadhesive according to claim 1, wherein at least one of saidpolypropylene glycols has originated from a DMC catalyzed preparationprocess.
 5. Pressure-sensitive adhesive according to claim 1, whereinsaid at least one polypropylene glycol triol is prepared by DMCcatalysis.
 6. Pressure-sensitive adhesive according to claim 1, furthercomprising formulating ingredients selected from the group consisting ofcatalysts, ageing inhibitors (antioxidants), light stabilizers, UVabsorbers and rheological additives.
 7. Process for preparing thepressure-sensitive adhesive of claim 1, comprising a) charging a firstvessel (A) with a premixed polypropylene glycol component comprising acombination of at least one polypropylene glycol dial and at least onepolypropylene glycol triol and charging a second vessel (B) with anisocyanate component comprising at least one aliphatic or alicyclicpolyisocyanate having a functionality of less than or equal to three,optionally also charging said first or second vessel, or both of saidvessels, with one or more formulating ingredients selected from thegroup consisting of catalysts, ageing inhibitors (antioxidants), lightstabilizers, UV absorbers and rheological additives, b) conveying thepolyol component and the isocyanate component via pumps through a mixinghead or mixing tube of a multi-component mixing and metering unit, tomix them to form a reactive polyurethane composition, c) applying thereactive polyurethane composition to a backing material, d) passing thebacking material coated with the reactive polyurethane compositionapplied thereto through a heating tunnel to cure the polyurethanecomposition to form a pressure-sensitive adhesive, e) winding thebacking material with the pressure-sensitive adhesive thereon up in awinding station.
 8. Process according to claim 7 wherein the preparationtakes place without solvent.
 9. Process according to claim 7, whereinthe preparation takes place without addition of water.
 10. Aself-adhesive article comprising the pressure-sensitive adhesive ofclaim
 1. 11. Method for the redetachable fastening without damage orresidue of articles having sensitive surfaces, made from polar plastic,glass or metal which comprises fastening said articles with thepressure-sensitive adhesive of claim
 1. 12. The pressure-sensitiveadhesive of claim 1, wherein said ratio of the number of hydroxyl groupsin the diol component to the number of hydroxyl groups in the triolcomponent is between 0.2 and
 5. 13. The pressure-sensitive adhesive ofclaim 1, wherein said ratio of the number of isocyanate groups to thetotal number of hydroxyl groups is between 0.95 and 1.05.
 14. Thepressure-sensitive adhesive of claim 1, wherein said ratio of the numberof isocyanate groups to the total number of hydroxyl groups is between1.0 and 1.05.
 15. The pressure-sensitive adhesive of claim 1, whereinsaid molecular weight of said triols which are combined with said diolshaving a molecular weight of less than or equal to 1000 is equal to orgreater than
 3000. 16. The pressure-sensitive adhesive of claim 2,wherein said diisocyanates are diisocyanates having asymmetricalmolecular structures.
 17. The pressure-sensitive adhesive of claim 3,wherein said polyisocyanate is isophorone diisocyanate.
 18. The processof claim 7, wherein said backing material to which said reactivepolyurethane composition is applied is moving at constant speed duringsaid application.
 19. The method of claim 11, wherein said articles areselected from the group consisting of magazines, newspapers, books andletters.